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Thread: Teensy 4.0 USB Host hardware connection Q's

  1. #1
    Junior Member
    Join Date
    Dec 2019
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    1

    Teensy 4.0 USB Host hardware connection Q's

    I'm making a USB host using the Teensy 4.0 and I think I've worked out details, but have a few lingering questions I'm making educated guesses about.

    I'm using a PTC fuse, a TVS diode and 100uF between the 5V that powers the Teensy and VBUS and TVS diodes on the D+ and D- lines

    1) Is there no need for any termination resistors in series with the D+ D- lines?
    2) Any need for common mode chokes in series with the D+ D- lines? I see some USB designs don't bother with chokes or beads or termination, but others do.
    3) I have the same question regarding adding bead in series on the VBUS after the fuse. And if a bead is recommended, what frequency would we be filtering. Is there a recommended inductance?
    4) Any advantage to using a current limiting switch vs a resettable PTC fuse on VBUS IF that IC switch is high by default anyway? Perhaps an advantage to having this switch turn on AFTER the Teensy boots up rather than when the 5v on the main board turns on?

    5) Was there a connection scheme in mind when putting these where they are on the bottom side with SMT pads?
    Working on connecting D+ D- using right angle header soldered to the SMT pads. We'll see how that works out. A tiny flexible cable is still possible.

    Thanks for any thoughts and advice.

  2. #2
    Senior Member
    Join Date
    May 2015
    Location
    San Francisco
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    211
    If you haven't seen it yet, check out the Teensy 4.0 breakout board and USB host board I made in this thread:

    https://forum.pjrc.com/threads/57672...Breakout-Board

    It copies the circuit from the T3.6 which has been very robust for me. The current limiting switch lets you enable/disable power on command but also provides ESD protection to the data pins which might be valuable in some environments and with hot plugging. I don't see any reason to add additional components to the data lines.

    I don't have the equipment to do a proper eye diagram on the data lines, but it seems to be working well. If I do yet another spin, I'd update the board to follow the layout recommendations in the TPDS3104 datasheet more closely.

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